1. Field of Invention
This invention relates to an integrated assembly of devices for providing building heating, ventilation cooling, fresh air ventilation, and air conditioning; and to improvements in controls for operating these devices.
2. Relevant Prior Art
The use of windows and doors to admit cool night air to improve the comfort and air quality of the interior of dwellings is a practice with origins in antiquity. The physical principle is to create a heat exchange between cool nighttime outside air and warmer surfaces of interior building components having significant mass such as masonry, wall and ceiling finishes, concrete floors, and furnishings. During nighttime cool outside air removes heat from the warmer surfaces. During daytime the cool surfaces of building components absorb heat from indoor air to keep the interior air temperatures lower. The cool surfaces also contribute to comfort by providing a lower mean radiant temperature, such that the human body radiates heat at a greater rate than if surrounded by warmer surfaces.
Effective use of outside air for cooling can also reduce the required capacity of air conditioners and reduce their energy consumption by reducing cooling load. In mild climates ventilation cooling can eliminate the need for compressor-based air conditioning. The most favorable outcome of the widespread use of ventilation cooling is the reduction of the peak electric load and mitigating the need to construct new power plants.
Whole-house fans have been used for several decades to provide a means of improving air exchange and circulation between indoors and outdoors; controls for these devices are typically switches, timers, and manually operated speed controls. Their relative simplicity is also a drawback. Whole house fans move air from indoors to outdoors, creating a negative indoor pressure, and rely on the operation of windows to admit air to the indoor spaces. Since this air is not filtered, dust and pollens are also admitted.
High noise levels produced by whole house fans is often objectionable.
There are also other concerns. The use of windows to provide nighttime ventilation compromises home security and requires active participation of dwelling occupants and. ventilation fan operation cannot be automated if windows must be manually opened to admit outside air. A ventilation cooling system produced by ZTECH of Rancho Cordova, Calif. (U.S. Pat. No. 5,065,585) eliminates the need to open windows. The ZTECH system provides outside air ventilation using a heating/cooling system blower and a damper with an air filter. The damper (U.S. Pat. No. 5,096,156) is connected to the intake of the blower, which supplies air to rooms of a building through ducting. In a first position of the damper, a passageway connects the blower unit to a building return air duct, thereby re-circulating indoor air for heating or air conditioning. The damper switches to a second position for ventilation cooling. In this second position a first passageway of the damper connects the blower to an outside air intake, thereby pressurizing the building with outside air. In this second position building air pressure is relieved through a second damper passageway that connects the building return air duct to a vented attic or the outdoors. In this manner the blower distributes filtered outside air to all rooms using the same ducts as used by the heating and cooling system.
The ZTECH system, and another system described in U.S. Pat. No. 5,902,183, utilize controllers that measure indoor and outdoor air temperatures and use these measurements to control when the ventilation systems should be operated. Both systems ventilate with outside air when outdoor air temperature is cooler than indoor air temperature by a selected temperature differential, and as long as the indoor air temperature is above a fixed low-limit temperature setting. Both systems also use controls that are separate from building heating and cooling system controls. Field studies conducted on homes equipped with the ZTECH system showed that homeowners lacked an understanding of how the ventilation systems worked and how they could be used to reduce energy use and improve comfort, A fixed indoor low-limit temperature setting employed by the ZTECH controls can cause excessive cooling on mild or cool days. Also, the controls provide no feedback to encourage lower indoor temperature settings that would avert air conditioner use on hot days.
Until recent years, normal leakage through gaps in construction assemblies has been sufficient to maintain indoor air quality at healthy levels in dwellings. Modern building standards and construction practices intended to conserve energy have resulted in much tighter buildings with less leakage. Several states have adopted regulations that require mechanical ventilation to exhaust indoor contaminants including carbon dioxide, carbon monoxide, excessive moisture, indoor allergens, and volatile organic compounds given off by carpeting and other building materials. Devices available to meet mechanical ventilation requirements include continuously operated bathroom fans, heat recovery ventilators, and systems that duct outside air into heating/cooling system return air ducts. In the latter category, Lipidex produces an AirCycler™ air handler system, U.S. Pat. Nos. 5,547,017 and 5,881,806, that includes an outside air duct connected between the return air plenum of a forced air heating unit and an outside air intake. A controller operates a motorized damper in the outside air duct and cycles the heating unit blower to provide fresh air. To its credit, the Lipidex system distributes fresh air to all conditioned spaces, but because this system mixes a large volume of re-circulated air with outside air, it must move more air and uses more fan energy than a system that ventilates with 100% outside air. Neither this system, nor bathroom fans, nor heat recovery ventilators move sufficient air to provide effective ventilation cooling.
A physical law that describes performance of centrifugal fans dictates that motor power demand varies with the cube of the airflow rate. High energy use, as well as noise problems, can be mitigated by employing a fan that delivers only the amount of air required to meet heating, cooling, and ventilation requirements.
Electronically commutated, variable speed, motors (ECM's) have been used to operate fans in heating and cooling systems for over a decade. These motors can be programmed to maintain constant airflow over a wide range of external static pressure, and allow the airflow to be varied by external controls. ECM's are much more efficient at low speeds than induction motors with multiple speed taps, and have been applied to provide continuously variable air delivery with heat pump systems such as the Trane XV-1500 and the Carrier Hydrotech 2000. ECM's have not previously been employed with outside air ventilation systems. ECM's are used in some variable speed gas furnaces, but current gas furnace technology does not allow airflow to be varied by more than 20%. Thus furnace fans must be cycled on and off when heating loads are low, and energy savings from motor speed reduction are much smaller than what could be achieved if airflow could be varied with heating load. Energy-saving heating and cooling thermostats that allow indoor temperatures to be scheduled over a 24 hour period are commonplace and can be used to reduce energy use. However, the scheduling features of these thermostats frequently go unused because they are not understood. Typically, a multitude of keystrokes are required to both enter and view time/temperature schedules. Also, thermostat displays do not adequately explain the meaning of their various settings.
Utility peak capacity shortages are reaching crisis proportions in areas of the U.S. Many utilities have undertaken programs to cycle air conditioning equipment off during periods of high peak demand. Conventional thermostats have no provisions for preventing operation specifically during utility peak power use periods or during power shortage alerts.